Summary:
The apparent molecular mass of the enzyme was determined by SDS-PAGE [Littlejohn03] . In mammals this monomeric enzyme is present in most tissues with the exception of liver, which contains tryptophan 2,3-dioxygenase. Catalytic differences between these two enzymes have been shown [Basran08]. The enzyme has been reviewed in [Rafice09] and [King07a].

The crystal structure of this enzyme has been determined [Sugimoto06].

A third enzyme indoleamine 2,3-dioxygenase-2 has been described in mouse. It is expressed in liver, kidney and in the reproductive system. It differs from this enzyme in its selectivity for some inhibitors. Its biological function remains to be determined [Ball09].